Question

At the starting gun, a runner accelerates at 1.9 m/s2 for 5.2 s. The runner’s acceleration is zero for the rest of the race. What is the speed of the runner at t = 2.0 s?

Answer 1

Answer: 3.8m/s

Explanation: he accelerates 5.2s ,but we know that:

vf=vo+at , vo=0 , t=2s so : vf = 1.9*2 = 3.8m/s

Answer 2

`3.8\text{m}/ \text{s}^2`

Step-by-step explanation:

Given: At the starting gun, a runner accelerates at 1.9 m/s2 for 5.2 s. The runner’s acceleration is zero for the rest of the race.

To Find: the speed of the runner at t = 2.0 s.

Solution:

initial speed of runner(
`\text{u}`) =
`0`
`\text{m}/ \text{s}^2`

acceleration for first 5.2s of race=
`1.9`
`\text{m}/ \text{s}^2`

to find speed of runner at ,
`\text{t}=2\text{s}`

Using first equation of motion,

`\text{v}=\text{u}+\text{at}`

putting values in the equation

`\text{v}=0+1.9*2`

`\text{v}=3.8`
`\text{m}/ \text{s}^2`

So,

The speed of the runner at
`\text{t}=2\text{s}`, is
`3.8\text{m}/ \text{s}^2`